The present invention relates to a method of inhibiting formation of unburned substances, such as CO and hydrocarbon, in incinerators for incinerating municipal refuse, industrial wastes and the like, and to incinerators for use in practicing the method.
Throughout the specification and the appended claims, the right-hand side of FIGS. to 7 and FIG. 15 will be referred to as "front," the left-hand side thereof as "rear," the upper side of FIGS. 5 and 7 as "left" and the lower side thereof as "right."
Municipal refuse, industrial wastes and the like are incinerated using incinerators, for example, like the one shown in FIG. 15. With reference to this drawing, the refuse incinerator has in its interior a primary combustion chamber 10, a secondary combustion chamber 11 above the chamber 10, a gas discharge channel 2 for guiding a combustion gas produced in the secondary combustion chamber lI to an unillustrated gas outlet, a stepped grate 13 disposed within the primary combustion chamber 10 and inclined forwardly downward, and a burner 14 provided at the rear side of the inclined grate 13 adjacent to the upper end thereof and obliquely directed forwardly downward. Although not shown, an exhaust heat recovery device and an exhaust gas cooling heat exchanger are arranged in the vicinity of the gas outlet of the gas discharge channel 12.
Refuse R is placed on the stepped inclined grate 13 within the primary combustion chamber 10 and burned by the burner 14 with primary air supplied from below the grate 13. A secondary air supply nozzle 15 extends through and is mounted on the front wall of the secondary combustion chamber 11.
The combustion gas resulting from the incineration of the refuse R passes through the gas discharge channel 12, and is cooled by passing through the unillustrated exhaust heat recovery device and the heat exchanger, then discharged from the gas outlet as a combustion exhaust gas and sent to an unillustrated exhaust gas treating apparatus.
The incineration of the refuse R involves the problem of locally increasing the temperature to produce NOx and clinker due to the fusion of ash. To obviate this problem, a nozzle 16 directed downward may be provided in an interior upper portion of the secondary chamber 11 for sprinkling cooling water downward.
However, the incineration of refuse with the incinerator encounters the following problem. Since the refuse to be handled in recent years has a higher calorific value, large quantities of volatiles are released from refuse R in the rearward portion of the primary combustion chamber 10 of the incinerator, forming flame F and combustion gas which ascend this portion of the chamber 10. The amount of primary air supplied from below the rearward portion of the grate 13 is nevertheless insufficient for the complete combustion of the large quanties of volatiles, causing incomplete combustion and permitting large amounts of unburned substances to ascend along with the flame F and combustion gas. While an excess of air needs to be supplied to the forward portion of the grate 13 from below in order to promote combustion of char resulting from the release of volatiles and to burn the unburned substances in ash, excessive air A not contributing to the combustion of the unburned substances in the ash ascends the forward portion of the primary combustion chamber 10. The flame F, unburned gas and excessive air A remain incompletely mixed even in the secondary combustion chamber 11, and the unburned gas is discharged as it is along with the combustion exhaust gas. The unburned gas contains a large amount of dioxin precursor, which forms highly toxic dioxin in the combustion exhaust gas, and the dioxin is released to the atmosphere.